Bark-Applied Chemicals to Control EAB

Research Issue

Since the discovery of the emerald ash borer (EAB) in Michigan in 2002 it has been realized that firewood and logs are two of the main pathways by which EAB has been moved to new location by humans. The current federal quarantine regulates movement of ash firewood and logs in all infested states. People have wondered if EAB could be controlled with an insecticide spray or dip while still under the bark of infested firewood and logs. It was thought that insecticides applied to the bark could kill EAB life stages given that larvae feeds in the cambial region just under the bark, and pupates in either the outer sapwood or the outer bark. We designed studies to address this question.

Our Research

In one study, we cut log sections from EAB-infested ash trees during winter and spring and then sprayed different insecticides on the bark surface to kill EAB. We tested imidacloprid, bifenthrin, and permethrin. The chemicals were applied once or twice approximately one month before adult emergence, or once or twice approximately two weeks before adult emergence was expected to begin.

Overall, all three chemicals were very effective in reducing the number of EAB adults that emerged from the treated logs. Logs that received two chemical applications had the highest mortality, while timing of application did not significantly affect EAB mortality.

In another study, we compared different concentrations of imidacloprid and borate solutions for killing EAB in infested logs. We cut logs from infested ash trees and either dipped or sprayed them with solutions of 0.01% imidacloprid or various concentrations of borate. No EAB adults emerged from logs that were dipped or sprayed with imidacloprid. However, EAB did emerge from logs treated with borate. Nevertheless, EAB emergence from the highest concentration of borate tested (5.52%), was significantly lower when compared to untreated logs.

Expected Outcomes

Our results will be useful to regulatory personnel and resource managers when setting guidelines for sanitizing infested ash logs. Our findings indicate that when logs are treated with imidacloprid, bifenthrin, or permethrin, EAB adult emergence is significantly reduced and fine tuning of the concentrations and application methods could eliminate EAB emergence completely. Borate at higher concentrations should also be investigated as an inexpensive alternative for reducing EAB adult emergence from logs.